1. Field of the Invention
The invention is in the field of food, pharmacy and health products development. The invention relates to a method of producing a nanofibrillar cellulose as a dietary fiber, especially a nanofibrillar cellulose with high absorptivity to fat and cholate.
2. Description of the Related Art
Dietary fiber plays an important role in maintaining the health of the digestive system and is also known as “the seventh nutrient”. Dietary fiber has great water absorption capacity, can increase the volume of feces in intestinal tract, increase the transport rate of feces, and decrease the contact time between harmful substance and intestinal wall. Dietary fiber can also adsorb the harmful substances to facilitate their excretion. Research has shown that intake deficiency of dietary fiber has direct correlation with the incidences of carcinoma of large intestine. The size of a dietary fiber directly correlates with its function. Nanocellulose is in the scale of nanometer. The size of nanocellulose is usually in 20 to 50 nm, and the length of nanocellulose is 100 to 150 nm. Different from traditional microcellulose, the crystal structure of nanofibrillar cellulose is broken, the accessibility to surface molecules is increased, and a large quantity of hydroxyl groups are activated.
Currently, nanocellulose is used and developed rapidly in the polymer material field, however, there is no nanocellulose used as dietary fibers in food, medicine and health products. Compared with common dietary fibers, nanofibrillar cellulose has several benefits, such as larger specific surface area and higher accessibility. It has been reported that there is a close correlation between the size of dietary fiber and its physicochemical and physiological properties. The smaller the size of a dietary fiber, the bigger the capacity in water and lipid absorption. It is shown that the smaller size of dietary fiber can better increase wet weight of feces and fecal contents, improve defecation, and adsorb fat and cholate. Existing technologies for making nanocellulose fiber use toxic reagents, strong oxidants, strong acids and bases, which causes pollution to the environment. The nanocellulose fiber made from the existing technologies cannot be used as dietary products.
To destroy the crystalline structure of cellulose and activate/enhance the reactivity of cellulose, strong oxidants, strong acids and bases are often used to pretreat lignocelluloses in the production of macromolecule material—nanofibrillar cellulose. These chemical methods not only cause pollution to the environment, but also generate large amount of by-products. Nanofibrillar cellulose made by these methods cannot be used in food, medicine and health products.
The methods for preparation of nanofibrillar cellulose include physical methods, such as high pressure homogenization and chemical-mechanical method; chemical methods, such as acid hydrolysis, base hydrolysis and ionic liquid dissolution; and the method of electrospinning. Most of nanofibrillar celluloses are prepared by hydrolysis method using sulphuric acid. However, the sulphuric acid hydrolysis has a number of drawbacks, such as the generation of a large amount of waste acid and impurity in the production process, strict requirement for reaction equipment and difficulty in waste recycling. Compared with chemical hydrolysis method, the present invention has many advantages, such as mild reaction conditions, high specificity, safe production process, and usage of simple and safe raw reagents. Nanofibrillar celluloses made by the invented method can be used in food, medicine and health products.
The present invention uses steam flash explosion technique to activate cellulose fibers. The steam flash explosion not only removes most of hemicelluloses and part of lignin, but also effectively destroys the crystal structure of cellulose, which results in increased accessibility and reactivity in activated cellulose, making it ready for downstream enzymatic hydrolysis and further modification. Most dietary fibers are hydrophilic and not effective at absorbing oil and cholate from the mixture of oil and water. It is shown that the modification of surface hydrophobicity of nanocellulose using octenyl succinic anhydride or glycidyl methacrylate can improve absorptivity to oil and cholate, and the modified nanofibrillar cellulose can be used as dietary fibers in the food industry.